Modern-era mobile phones, handsets, tablets, mobile terminals, mobile devices, or user equipments have evolved into powerful image- and video-processing devices, equipped with high-resolution cameras, color displays, and hardware-accelerated graphics. With the explosive growth of mobile devices, like android, iPhone, mobile based multimedia visual services are enjoying intense innovation and development. Application scenarios of mobile visual search services can be location based services, logo search, and so on, where one image or multimedia sent from a mobile device is matched to another one stored in a database or an image repository. First deployments of mobile visual-search systems include Google Goggles, Nokia Point and Find, Kooaba, and Snaptell.
The image queries sent by mobile devices through a wireless network are usually computationally expensive, requiring prohibitively high communication cost, and cannot support real time operations. In popular applications where a mobile device captures a picture of certain objects and sends it as a query over a wireless network to search a large repository, reducing the bit rate while preserving the matching accuracy is a main concern and a main focus of the standardization effort under MPEG.
Visual descriptors or image descriptors can be used as queries instead of an image for visual search purposes. However, for mobile devices, visual descriptors are usually still very heavy as they comprise of hundreds or thousands of scale and rotation invariant feature points, as well as their locations. An example feature point of scale-invariant feature transform (SIFT) comprises of 128 dimension with 2048 bits. Another example feature point of speeded up robust features (SURF) comprises of 64 dimension with 1024 bits. Reducing the size of the feature points may compromise the performance of the searching and matching accuracy in visual search services.
On the other hand, a point set of the images instead of the complete image may be sent by a mobile device to search the image repository. A point set may be sent at the same time or separately from sending the feature points of an image for visual search. Therefore a point set can be used to search and match images in visual search as well, in addition to the feature point search.
It is still a main concern for reducing the bit rate while preserving the matching accuracy with the use of feature points and point sets.